refactor: Declare g_zmq_notification_interface as unique_ptr

Ensures better memory safety for this global. This came up during
discussion of the following commit, but is not strictly required for its
implementation.

Author: TheCharlatan

src/init.cpp

@@ -328,9 +328,8 @@ void Shutdown(NodeContext& node)
 
 #if ENABLE_ZMQ
     if (g_zmq_notification_interface) {
-        UnregisterValidationInterface(g_zmq_notification_interface);
-        delete g_zmq_notification_interface;
-        g_zmq_notification_interface = nullptr;
+        UnregisterValidationInterface(g_zmq_notification_interface.get());
+        g_zmq_notification_interface.reset();
     }
 #endif
 
@@ -1428,7 +1427,7 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     g_zmq_notification_interface = CZMQNotificationInterface::Create();
 
     if (g_zmq_notification_interface) {
-        RegisterValidationInterface(g_zmq_notification_interface);
+        RegisterValidationInterface(g_zmq_notification_interface.get());
     }
 #endif
 

src/zmq/zmqnotificationinterface.cpp

@@ -39,7 +39,7 @@ std::list<const CZMQAbstractNotifier*> CZMQNotificationInterface::GetActiveNotif
     return result;
 }
 
-CZMQNotificationInterface* CZMQNotificationInterface::Create()
+std::unique_ptr<CZMQNotificationInterface> CZMQNotificationInterface::Create()
 {
     std::map<std::string, CZMQNotifierFactory> factories;
     factories["pubhashblock"] = CZMQAbstractNotifier::Create<CZMQPublishHashBlockNotifier>;
@@ -68,7 +68,7 @@ CZMQNotificationInterface* CZMQNotificationInterface::Create()
         notificationInterface->notifiers = std::move(notifiers);
 
         if (notificationInterface->Initialize()) {
-            return notificationInterface.release();
+            return notificationInterface;
         }
     }
 
@@ -198,4 +198,4 @@ void CZMQNotificationInterface::BlockDisconnected(const std::shared_ptr<const CB
     });
 }
 
-CZMQNotificationInterface* g_zmq_notification_interface = nullptr;
+std::unique_ptr<CZMQNotificationInterface> g_zmq_notification_interface;

src/zmq/zmqnotificationinterface.h

@@ -23,7 +23,7 @@ class CZMQNotificationInterface final : public CValidationInterface
 
     std::list<const CZMQAbstractNotifier*> GetActiveNotifiers() const;
 
-    static CZMQNotificationInterface* Create();
+    static std::unique_ptr<CZMQNotificationInterface> Create();
 
 protected:
     bool Initialize();
@@ -43,6 +43,6 @@ class CZMQNotificationInterface final : public CValidationInterface
     std::list<std::unique_ptr<CZMQAbstractNotifier>> notifiers;
 };
 
-extern CZMQNotificationInterface* g_zmq_notification_interface;
+extern std::unique_ptr<CZMQNotificationInterface> g_zmq_notification_interface;
 
 #endif // BITCOIN_ZMQ_ZMQNOTIFICATIONINTERFACE_H